Hey,

You can collect fragments of the other summons and just unlock them to have them available for battle. They are important, as if you use them the right time, you might be able to avoid getting hit by some aoe mysteries. You can focus towards a summon for now to level it up, because if you try and level up all of them, they'll starve and the chakra supply will be really hard to handle, thus the powering up boost won't be given there. Additionally, it's good to have one strong enough summon other than 3 ones that would get one shot. Once the clan becomes more active and you collect enough supplies, you can try and feed the other ones as well. Also, each summon does consume 7% of the total chakra. I'd suggest you to always try and submit the chakra as whole set and not only as single. Try to trade with each other in your clan and and at some point you'll have enough chakra for the other summons as well.

Hope that helps!